Several different kinds of such-power transmission systems are known in the art.
An example of such systems is described in Patent Publication DE-3 303 886. This publication describes and illustrates a planetary gear arrangement which includes a sun wheel (13) connected to a drive shaft (12), at least two planet wheels (18, 19), and a ring wheel (20) which functions to drive an output shaft (22) while using an hydraulic torque converter (27, 28, 29).
The torque converter comprises two hydraulic pumps (27, 28); each co-acting with its individual planet wheel (18, 19), and connected hydraulically via a hydraulic conduit system (29).
Patent Publication U.S. Pat. No. 3,866,490 describes and illustrates a transmission system which uses a planet gear arrangement to regulate the speed of an output shaft in relation to an input shaft.
More specifically, the input shaft (11) is connected directly for driving the planet wheel carrier (16) via a connection sleeve (17), and therewith the planet wheels (18, 19).
The outputs of this planetary gear assembly (15) comprise the ring wheel (20) on the one hand and the sun wheel (21) on the other hand.
A shaft (29) co-acts with a gearwheel (30) which, in turn, co-acts with a gearwheel (31) and drives an hydraulic unit (33) with variable displacement.
Patent Publication U.S. Pat. No. 4,750,381 teaches an hydromechanical transmission that can be used as an efficient, continuously variable transmission with the aid of a differential mechanism.
This publication discloses the use of an hydraulic transmission mechanism, a mode selecting mechanism, a locking mechanism and a clutch mechanism.
It will be noted in particular that the input shaft (11) acts on the planet wheels, and that the sun wheel is coupled directly to a pump unit (5) having a fixed pump/motor displacement, which is coupled hydraulically to a variable displacement unit (7).
The publication also describes the use of a locking mechanism (11) related to the sun wheel shaft and a clutch (12) belonging to the unit (7).
Patent Publication GB-A 1 174 778 describes and illustrates a transmission mechanism which is particularly adapted for automotive vehicles, said transmission mechanism being of the kind in which power is divided between a mechanical path and an hydrostatic path.
As with the present invention, this transmission mechanism is adapted particularly for use with cross-country vehicles, such as tractors, and carries out a major part of its work under conditions that require a low speed range and a high torque.
Patent Publication GB-A 1 379 213 illustrates and describes an hydromechanical transmission system that is able to offer a plurality of driving speed ranges.
There is used to this end an input shaft (10) and an output shaft (12), and a duplicated planetary gear arrangement (4) and an hydrostatic transmission (16) that can co-act with the two planetary gear arrangements (14).